server.js

const express = require("express");
const path = require("path");
const bodyParser = require("body-parser");
require("dotenv").config();
const fs = require("fs");
const { GoogleGenerativeAI } = require("@google/generative-ai");

const app = express();
const PORT = 3000;

// 파일 경로
const HISTORY_FILE = path.join(__dirname, "conversation.json");
const MAX_HISTORY_LENGTH = 10; // 대화 기록 최대 길이 (사용자 질문 + AI 답변 = 1세트)

// 미들웨어
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(express.static(path.join(__dirname, "public")));

// Gemini 모델 초기화
const apiKey = process.env.GEMINI_API_KEY;
if (!apiKey) {
  console.error("GEMINI_API_KEY is not set in the .env file.");
  process.exit(1);
}
const genAI = new GoogleGenerativeAI(apiKey);

const model = genAI.getGenerativeModel({
  model: "gemini-1.5-flash",
});

const generationConfig = {
  temperature: 1,
  topP: 0.95,
  topK: 64,
  maxOutputTokens: 8192,
  responseMimeType: "text/plain",
};

// 대화 기록 불러오기
function loadHistoryFromFile() {
  try {
    if (fs.existsSync(HISTORY_FILE)) {
      const data = fs.readFileSync(HISTORY_FILE, "utf8");
      if (data.trim() === "") {
        return [];
      }
      return JSON.parse(data);
    }
  } catch (error) {
    console.error("Error loading conversation history:", error);
  }
  return [];
}

// 대화 기록 저장
function saveHistoryToFile(history) {
  try {
    const historyToSave = history.slice(-MAX_HISTORY_LENGTH * 2);
    fs.writeFileSync(HISTORY_FILE, JSON.stringify(historyToSave, null, 2));
  } catch (error) {
    console.error("Error saving conversation history:", error);
  }
}

// 루트 경로
app.get("/", (req, res) => {
  res.sendFile(path.join(__dirname, "public", "index.html"));
});

// 대화 API
app.post("/ask", async (req, res) => {
  try {
    const { prompt } = req.body;
    if (!prompt) {
      return res.status(400).json({ error: "Prompt is missing." });
    }

    const history = loadHistoryFromFile();

    const chatSession = model.startChat({
      generationConfig,
      history,
    });

    const result = await chatSession.sendMessage(prompt);
    const answer = result.response.text();
    console.log("AI Answer:", answer);

    const newHistory = [
      ...history,
      { role: "user", parts: [{ text: prompt }] },
      { role: "model", parts: [{ text: answer }] },
    ];

    saveHistoryToFile(newHistory);

    res.status(200).json({ answer });
  } catch (error) {
    console.error("Error during AI interaction:", error);
    if (error.message.includes("API key not valid")) {
        return res.status(401).json({ error: "Invalid API key. Please check your .env file." });
    }
    res.status(500).json({ error: "Internal Server Error" });
  }
});

// 대화 기록 조회
app.get("/history", (req, res) => {
  try {
    const history = loadHistoryFromFile();
    res.status(200).json({ history });
  } catch (error) {
    console.error("Error reading history:", error);
    res.status(500).json({ error: "Failed to load history." });
  }
});

// 서버 시작
app.listen(PORT, () => {
  console.log(`Server running at http://localhost:${PORT}`);
  console.log("Please set your GEMINI_API_KEY in the .env file.");
});